Image Processing Reference
Fig. 17.2 Relationship between urban area and urban population as a function of Gross Domestic
Product per capita
Figure 17.2 below shows a scatter plot of the log of the area of urban clusters
versus the log of the corresponding population of urban clusters around the world.
This kind of information is easily extracted from an overlay of the nighttime imag-
ery on a population density dataset such as LandScan (Dobson et al. 2000 ). Each
point in the scatter plot is a 'blob' of light that is referred to as an urban cluster. The
regression equations can be used to estimate the population of an urban cluster of
unknown population or the estimated value can be compared to the actual value to
provide a scale-adjusted measure of the extent to which that city suffers from urban
sprawl (Sutton 2003 ). International comparisons of these kinds of regression equa-
tions show that countries with lower Gross Domestic Product per capita (GDP/
Capita) tend to have the same log-log relationship between areal extent and popula-
tion; however, the intercept is higher.
This implies that a city of 800 km 2 in a poor country will have a higher aggregate
population density than a city of 800 km 2 in a developed country. This makes sense
when one considers how the availability and use of the automobile in developed coun-
tries has enabled urban populations to spread out to suburbs and beyond to exurbia.
For a more detailed description of the use of these kinds of regression equations to
estimate the populations of all the urban areas of the world see Sutton ( 1999 ).